Devices for increasing luminosity



March 28, 1961 Filed Dec. 7, 1956 J. c. VULMIERE ETAL 2,977,497

DEVICES FOR INCREASING LUMINOSITY 3 Sheets-Sheet 1 IN v EN T0 Rs ncques cuwas VULMIERE HUG- UETTE VULMIERE MAX FOURESTIER ATTORN EYS March 28, 1961 J. c. VULMIERE ETAL 2,977,497

DEVICES FOR INCREASING LUMINOSITY Filed Dec. 7, 1956 3 Sheets-Sheet 2 INVENT R :mcguss cLAuOE VuLM/ERE UETTE V L ERE FOURESTI' BY 4 I ATTOR NE YS March 1961' J. c. VULMIERE ETAL 2,977,497

DEVICES FOR INCREASING LUMINOSITY Filed D60. '7, 1956 5 Sheets-Sheet 5 INVENTORS TACQUES. CLAUDE VULHIERE Y HUG-UETTE VVLMIERE MAX FDVRESTIER y m ATTORNEYS DEVICES FOR INCREASING Jacques Claude Vulmiere and. Huguette Vulmiere, ne Grangaud. Pre-Saint-Gervais, and Max Fourestier, Van'ves,'France, assignrs to Centre National de la Recherche Scientifique, Paris, France, a corporation of France Filed Dec. 7, 1956, Ser. No. 626,874 I Claims priority, application France Dec. 9, 1955 11 Claims. (Cl. 313-112).

'Ihepresent invention relates to a, device for increasing the luminosity of incandescent lamps having polished emitting surfaces, for example with tungstenfilaments or tapes, or with diffusing emitting surfaces, for example with opaline bulbs, with Nernst or Globar rods.

The invention also enables the luminosity to be made uniform, particularly in the caseof the tungsten filament lamps of the type used in cinematograph projectors.

Up to the present time, certain well-known optical methods have been proposed inorder. to obtain an increasein the efliciency ofan'incandescent source. Be: ing providedsolely for lamps withgcoiled. tungsten. filamerits, they are intended to form an. imageof] the filament on itself in order toattempttoflll in thejga'ps. be.- tween the filament spirals.

T othis end, there is. employed either a mirror which is centered on thefilament and having anopening equal to that. of the condenser which is placed in front of the source, or the bulb itself is partly. silvered, provided-ah ways that it is spherical and centered on the filament.

In practice, under the best conditions of; construction, the average increase in luminosity obtained does,

not exceecl 30%. This is. due to the fact that the existing types. of lamps being tightly coiled, there are very few and very smallgaps between the spirals of the filament, and also. that these gaps cannot be entirely covered by the inverted image of the filament, sinc e.; it is. not possible to obtain such a perfect uniformity of winding in spirals as would make the image identical with the object.

It has also been proposed'in the case of spherical bulbs, to silver them almost, entirely while forming, a window corresponding to the opening ofthe condenser; The silvering, thebulb and the filament-do, not-.how;

ever withstand the high temperatures to which, they are thussubjected, and it has therefore been proposed to enclose these lamps in an indestructible sphericaLcap ofsmall size, placed against. thebulb. However, this chamber forms in fact acalorimeter and theincrease in of the temperature rise. in'the' chamber which is not ventilated.

Thepresent invention has the feature in common with the above methods, of utilising reflecting systems around the source of light. As will be seen in the description which follows, however, the objects the numerical results, and the practical method of construction are very different.

speotrumand also outside this region It has already The present invention is applicable to a large rrumber of types of lamp in the region of the visible essential objects of the invention,

fl 2,917,497 Patented M nfifi .19 1...

ice

2 beenemployed under practical conditions by thepres-a ent-inventors with success.

It will be remembered that. the luminous energy of 'a; polished tungsten element at an absolute temperature'i'l is less than that of a black body at 'the samefternp' ture T. The same thing is true for a Nernst'or Glo filament.

1n the case of tungsten which, in the visible spectrum, is

It is one-third at about 1 micron, onerquarter at,.2. mi';i crons and one-fifth at about 3 microns. l

In the case of the Nernst filament whichisprefer'ably employed between 3 and 7 microns, this-idilfereilc is large, since in this region it attains one-tenth to. on twentieth. I I

This shows the great advantage which it. is possible to gain by transforminga given source to a. sourceeq alent to the black body of the same, surface areaand the same real temperature. M i

A substance suchas. tungsten. has, when hot, if --it-= is polished, a high reflecting power which is substantial i constant in the visible spectrum. and equaLto 0.5 afgt Whichit increases. rapidly in the near itifra-redandwrg;

ceeds 0.9 beyond 2 microns.

nomenon is found. asfar as its diffuse. refleeion fa is concerned, which is in thefvicinity, of l in then infra-red.

To sum up, whether it is polished or. diffusive, a filamentbrough up to incandescence. can becons ideredg at, the same time as a source possessing a luminousenergv" proper L, and, as a mirror: or a diffusing screenhaving'aa reflecting power R whenhot.

The above observations have. led' the. inventors .to-Ithe idea of constructing a devicefor increasing. the. luminosity of incandescent lamps, such as has been 'referredz to above. To this eud, it is proposed to. utilisethe lumi nous energy which is not. directly employed'by. the con denser to form the image ofthe filament. strictly-and exactly on itself, by means ofPa. suitable'optical sys? tern. If part of the reflected rays is locatedrin the direc tion of observation, the apparentluminosity of the co' e sponding part of the filamentbecomes "L(l--i-'R:) g lecting the losses .due to the optical system." This isthe sum-0f the luminosityproper of the filament andof-th luminosity of the image reflected by the filament.

If the optical device. enables thenumber of successive reflections on itself and. on the filament tobeineraseugi theapparent luminous energy of the filament will-tend? towards the limit:

For a given wave-length, the coefiicient of.increase, of the luminous energy will tend? For. R -0.5, towards, 2', For R'=0.75, towards 4 For R=0.9,j towards 10 In order however to obtain such an efficiency, the :op'ti-f cal device associated with; the, sonrcecohsidere'd a a mirror or as a diffusing screen should be capable of v-f' ingalarge numberof'multiple reflections, andlthisrwltli a minimum of loss dueto this device. This is one of the In other words, the invention consistsin transforming. the emi tting sourcejat: atrue temperature-T to,a sources hay 'g an identical surface area, the useful aperture. which can easily; attain. 60; the... properties, of

' 5 glissiqn' asvne in ma germs? vicinity of those of the black body at that same temperature T, practically unchanged, and this without substantial modification of the power required for the supply of the incandescent filament.

. In accordance with the invention, the device having a uniformly-distributed high luminosity, comprising a filament or strip and means for reflecting the light emitted by the filament in a desired direction, is characterised by the fact that the said reflecting means are surfaces of large dimensions, centered on the filament or the like, are non-diffusing and have a reflecting power as high as possible in the region of the spectrum employed, and that, with respect to the source, the said reflecting means are in a position such that the luminous energy is as close as possible to that of the black body at the same temperature.

In order to obtain the best results under the general conditions indicated above, the assembly of the elements of the device should be such that the spherical aberration in the vicinity of the centre of curvature is very small, which leads in practice to a diameter of the sphere greater than 60 mm. At the same time, the diffusion should be a minimum and the sphericity should in consequence be perfect with an excellent polished surface. The reflection factor of the system should be as close as possible to l in the field of the spectrum employed, which necessitates a suitable choice of the reflecting material to be deposited. The centering of the source in the sphere should be perfect. I In order to obtain these results, it is possible to couple together two metallic half-spheres on the internal surface of which there has been deposited a reflecting layer or coating.

It maybe preferable to replace the two metallic halfspheres by half-spheres of glass such as that known under the registered trademark Pyrex or, better still, by transparent optical silica which resists thermal shocks, the half-spheres being metallised as may be required on their convex or concave sides.

It is essential to provide an efficient cooling for the glass bulb, which absorbs practically all the infra-red rays beyond 2 microns, and this can easily be effected with the device in accordance with the invention.

The source of light may be a metallic filament or strip, preferably of tungsten, having in known manner a high strength in the vicinity of its supports. As diffusing sources, there may be employed either opalescent lamps or filaments with Nernst or Globar rods.

The accompanying drawings show various forms of embodiment of the devices in conformity with the invention. In these drawings:

Figs. 1 and 2 illustrate the case of a strip-filament lamp, respectively in a horizontal cross-section view and a view in perspective, of a first form of embodiment of the invention.

Figs. 3 and 4 show two views of an alternative form in cross-section made respectively along two planes at right angles.

Fig. 5 is a view in cross-section of a lamp in accordance with the invention which permits of an easy cooling, with out considerable bulk.

Fig. 6 is an alternative form of the device shown in Figs. 3 and 4.

Fig. 7 shows an alternative form of the device shown in Figs. 1 and 2.

Fig. 8 is a diagrammatic view of an assembly with an opaline source.

In the form of embodiment of Figs. 1 and 2, the inon the other hand, the radiation emitted by the strip in the direction of the mirror, which radiation has been reflected at least once on the mirror 2 and then on the strip 1. In order to collect this radiation under good conditions, whilst avoiding stopping-down to a cat's eye," the lens 5 is given an opening slightly less than that of the mirror 2. 7

As the luminosity of tungsten in the hot state does not follow Lamberts law, but varies with the incidence so as to reach a maximum towards 70, the angle of the axes of the mirror 2 and of the condenser 3 with XX is chosen or calculated so as to obtain a maximum luminosity by using the best portion of the curve of variation of the luminosity of tungsten as a function of the incidence for a given opening of beam.

The mirror 2 may be replaced by a lens 2' (see Fig. 7) and a plane mirror perpendicular to the axis forming an auto-collimator system on the filament. A colored glass 2" may be placed in a manner inclinable at will on the axis in front of the plane mirror, between the said mirror and the lens, that is to say in order to keep the beam parallel so as to cause the thickness of the glass passed-through to vary, to modify the coloration of the reflected beam and, in consequence, to modify the color temperature of the overall beam employed. In this way, there can be obtained a variable colored brilliance which is greater than the brillance of the filament itself.

When a tungsten filament is used as a source with a continuous spectrum, by employing an auxiliary monochromatic lamp with spectral lines, reference marks of pre-determined wave-lengths can be projected on the con tinuous base provided by the filament.

In accordance with the form of embodiment shown in Figs. 3 and 4, the lamp 6 has its filament 7 located at the centre of a spherical mirror 8; the filament is preferably provided with a number of rows of coils. The mirror is formed by two members 9 and 10, of metal, or of transparent silvered optical silica, the internal spherical surface of which is reflecting and is very precisely centered on the filament. Its radiusis made sufiiciently great for the aberrations of the images of the edges of the filament to be negligible, these images being formed in the vicinity of the centre of curvature. Cylindrical openings 11 and 12 permit of the passage of the base and of the upper portion of the lamp, together with the flow of cooling air.

The two members 9 and 10 are each provided with a flanged portion 13, 14 and are connected together for example by means of screws. This permits of easy dismantling for changing the lamp, whilst ensuring a correct position during re-assembly. A cylindrical opening formed in the members 9 and 10 provides the housing for a condenser 15. The socket of the lamp, not shown on the drawing, is provided with the desired adjusting devices which will permit of the perfect centering of the filament at the centre of the spherical mirror.

Fins 16 help in ensuring the cooling. This cooling can be further assisted by a forced ventilation which will follow the direction of the arrows F.

For large outputs, lamps with external bulbs can be used, such as shown in Fig. 5. The portion located in the interior of the reflecting sphere is of small dimensions and the cooling will be effected, not only by a flow of air following the path of the arrows F, but also by the movements of convection of the gas inside the bulb, of which a part 17, located outside the reflecting chamber, is in direct contact with the air.

This device is especially utilisable in cinematographic projectors; the spherical mirror transforms the source of light to a black body, fills in the gaps between the spirals and improves the uniformity. Thus the image is formed closer to the film by using only the central coils at high temperature. The coetficient of increase obtained is of the order to 4 to 5.

Fig. 6 relates to the case in which the source of light is a spherical bulb with a bunched filament (one single wilr f y-w ndfiumsfi. n ern l. sn er ealmie 'ron may, be used, leaving as openings only those required 'for the passage of the bulb and of the condenser. In certaincases, in order to reduce the overall bulk of the system, itis preferable to use, not av single sphere, but portions of. spheres having different radii, these various portions being accurately centered on the filament. A system of this kind is essentially formed by two spherical mirrors 18 and 19 of the same radius and an element 20 having asmaller radius. This element 20 has the same openings as the condenser 15. It does not play the same part as the-mirrors 18 and 19, but serves only to send back to the condenser the light flux which it receives; for that reason, it may be slightly polished.

This bunched filament device may be employed either for normal working:

In the visible spectrum; the mean luminosity is multiplied by about 3;

In the infra-red spectrum (towards 1- micron to 1.5 microns) the luminous energy is multiplied by about 4 or 5, which gives very good possibilities for infra-red projectors using receivers '1 with photo-electric cells or image transformers;

Or for working with excess voltage in the vicinity of the melting temperature of tungsten, there is obtained a luminosity in the red very close to that of the electric arc: this is a greater and important advantage in medical photography; for example with an endoscope or a retinograph, or a slot lamp.

A lamp with an opaline bulb 21 may be employed, for example for the enlargement of photographic negatives 22 (see Fig. 8), the summit of the lamp being centered on the mirror. There may also be employed as a source a lamp with a Nernst filament with its axis on the reflecting sphere; in accordance with the oxides employed for the rods, there is obtained a coeflicient of increase of to for the spectral region of 1 to 7 microns.

It can be seen that the device in accordance with the invention enables the luminosity of an incandescent lamp to be increased by observing a portion of filament or of strip which emits, in addition to its own radiation, a refiected radiation derived either from another portion of the filament or strip, or from the same portion of the filament or strip but after at least one reflection on a mirror.

It has been found that in all cases, the device in accordance with the invention ensures a very large number of multiple reflections with the minimum of loss inherent in the apparatus. In practice, the devices which have been described above generally enable the brilliance to be multiplied by a coeflicient comprised between 3 and 20, depending on the cases and the field of the spectrum in which the work is carried out.

The device in accordance with the invention finds its applications, inter alia in projectors, projection apparatus for cinemas, lighting devices for microscopes, endoscopes, profile projectors, slot lamps, retinographs, searchlights, electronic projectors for barrages, etc.

What we claim is:

1. An optical illuminating system having a high and uniform luminosity, comprising an incandescent element constituting a source of radiation; an envelope containing said element; means of optical quality in the path of visible radiation from said element for reflecting such radiation and forming a reflected image of said incan-. descent element strictly and exactly on said element, said means comprising a spherical optical surface of large dimensions perfectly centered on said incandescent element and having a radius such that spherical aberrations close to its center of curvature are substantially smaller than said incandescent element; and a condenser adapted to collect radiation from said source, the axis of said condenser intersecting the axis of said incandescent element at the center of curvature of said surface; whereby the total luminous energy collected by said condenser is they sum ofthe direct radiation;theretg;frormsajdgelem i i; and the multiple reflections by said; means of.- radiat; ion; from said element, and approximates that ofya, black; body at the same absolute temperature as saidelerne 2. An optical illuminating system'having a'- high a uniform luminosity, comprising an incandescent element constituting a source of radiation; an envelope contain ing said element; means of optical quality'in the path of. visible radiation from saidelement for reflecting such, radiation and forming a reflected image of said element strictly and exactly on said element, said means cprnprising a spherical optical surface of large dimensions penfectly centered on said element and having a radius such, that spherical aberrations close to its center of CllIYfl-gture are substantially smaller than said element, said; means including a lens'providing said spherical surface and aplane mirror positioned perpendicular to the axis, of said lens to form an auto-collimator system onsaid element; and a condenser adapted to collect radiation from said source of radiation, the axis of said condenser intersecting the axis of said element at the center of curvature of said spherical surface; whereby the total luminous energy collected by said, condenser is the sum of the direct radiation thereon from said element andthe mul-- tiple reflections by said means of radiation from said element, and approximates that of a black body at the same absolute temperatureas said element.

3. An optical illuminating system having ahigh and uniform luminosity, comprising an incandescent element constituting a source of radiation; an envelope containing said element; means of optical quality for forming a refiected image of said element strictly and exactly on said element, comprising a spherical opticalsurface of large dimensions perfectly centered on said element and having a radius such that spherical aberrations close to its center of curvature are substantially smaller than said element; said means including a lens providing said spherical surface, a plane mirror positioned perpendicular to the axis of said lens to form an auto-collimator system on said element, and a colored glass element disposed between said mirror and said lens, said colored glass element being inclinable with respect to the axis of said auto-collimator system; and a condenser adapted to cooperate with said source of radiation; the axis of said condenser intersecting the axis of said incandescent'element at the center of curvature of said spherical surface; whereby the total luminous energy collected by said condenser is the sum of the direct radiation thereon from said incandescent element and the multiple reflections by said means of radiation from said element, and approximates that of a black body at the same absolute temperature as said inelement, comprising a spherical optical surface of large' dimensions perfectly centered on said element and having a radius such that spherical aberrations close to its center of curvature are substantially smaller than said element; said means including a lens providing said spherical surface, a plane mirror positioned perpendicular to the axis of said lens to (form an auto-collimator system on said element, and a colored glass element disposed between said mirror and said lens, said colored glass element being inclinable with respect to the axis of said auto-collimator system; and a condenser adapted to cooperate with said source of radiation, the axis of said condenser intersecting the axis of said incandescent element at the center of curvature of said spherical surface; whereby the total luminous energy collected by said condenser is the sum of the direct radiation thereto from said incandescent element and the multiple reflections by said means of radiation from said incandescent element, and approximates that of a black body at the same absolute temperature as said incandescent element; said system further comprising an auxiliary mono-chromatic lamp for projecting reference marks of predetermined wave lengths on the continuous base derived from said incandescent element.

5. An optical illuminating system having a high and uniform luminosity, comprising an incandescent element constituting a source of radiation; an envelope containing said element; reflector means of optical quality in the path of visible radiation from said element for reflecting such radiation and forming a reflected image of said incandescent element strictly and exactly on said element, said means comprising a plurality of spherical mirror elements of the same radii having their radii centered on said source and being arranged symmetrically with respect to a plane of emission of radiation from said source; a spherical mirror having a smaller radius than said mirror elements; an emission window; the opening angle of said mirror being equal to the opening angle of said window; said mirror and said window lying across and being centered on said plane at opposite sides of said source; and a condenser for collecting radiation reaching said window, the axis of said condenser intersecting the axis of said incandescent element at the center of curvature of said mirror; whereby the total luminous energy collected by said condenser is the sum of the direct radiation thereto from said incandescent element and the multiple reflections by said reflector means of radiation from said inbody at the same absolute temperature as said incandes-' cent element.

6. An optical system as claimed in claim 1, said reflector means being substantially non-diffusing to said radiation and having substantially the maximum possible reflecting power for said radiation.

7. An'optical system as claimed in claim 1, said incandescent element being a single coiled tungsten element.

8. An optical system as claimed in claim 1, said incandescent element being a flat tungsten strip element.

9. An optical system as claimed in claim 1, said incandescent element being constituted by a plurality of coiled tungsten filaments.

10. An optical system as claimed in claim 1, said incandescent element being constituted by an electrical resistance rod filament.

11. An optical system as claimed in claim 1, said source of radiation being an opalescent lamp.

. References Cited in the file of this patent UNITED STATES PATENTS 1,239,371 Evans Sept. 4, 1917 1,863,152 .Barkey June 14, 1932 2,360,971 Parish Oct. 24, 1944 2,859,369 Williams et al Nov. 4, 1958 

